The present invention relates to improvements in a wire discharge machining method and apparatus that allows the shape of a machined workpiece to be predicted and displayed. Throughout the specification, by the phrase xe2x80x9cwire discharge machiningxe2x80x9d it is meant that an electric dischargexe2x80x94occurring between a wire electrode and a workpiecexe2x80x94machines the workpiece.
FIG. 8 shows a conventional wire discharge machining apparatus. In FIG. 8, this wire discharge machining apparatus comprises a workpiece 1, a wire electrode 2, a base board 3, an X table 6, a Y table 7, an X-axis servo amplifier 8, a Y-axis servo amplifier 9, a working fluid nozzle 11, a working fluid 12, a numerical control unit 13, a program analysis means 14, a locus movement control means 15, a program locus drawing means 16, a display unit 17, and a drawn locus 18.
The operation will be described below. In FIG. 8, the machining is performed by supplying a working electric power from a working power source, not shown, to a gap between the wire electrode 2 and the workpiece 1 and producing a discharge between them. In this case, the X table 6 and the Y table 7 are driven on the basis of a program stored in the numerical control unit 13, machining the workpiece into a desired shape. That is, the numerical control unit 13 issues a speed signal to the X-axis servo amplifier 8 and the Y-axis servo amplifier 9 to drive a servo motor, not shown, to move the X table 6 and the Y table 7, and move the workpiece 1 fixed in the base board 3 on the X table 6, so that the workpiece is machined.
FIG. 9 shows a positional relation between the wire electrode 2 and the workpiece 1 during the first cut (first machining), in which the center of the wire electrode 2 follows the course of the machining positions calculated by the program analysis means 14. The wire electrode center path is separated an offset value specified from that path calculated by a given program with an offset value of zero. Also, when the workpiece is removed by discharging, a gap produced between the wire electrode and the workpiece is called a discharge gap, the amount of gap being varied depending on the machining conditions.
A second cut (second machining) method has been disclosed as a common machining technique to finish the workpiece with higher precision by performing a second machining using an offset value varied in the same program. The positional relation between the wire electrode and the workpiece in the second machining is shown in FIG. 10. As the machining conditions for use with the second machining, the discharge gap and the offset value are set to the smaller values than with the first machining, to secure an allowance for machining in the second machining. A difference in the offset value between the nth machining and the (nxe2x88x921)th machining is called an nth correction amount. If the correction amount is not selected to be a suitable value, no discharge is effected at all, or conversely a short-circuit is caused, resulting in a situation of not machining the workpiece.
Assume the distance between the surface of wire electrode and the workpiece before machining to be L, the discharge gap at this time to be G, and the minimum gap between the workpiece and the wire electrode to prevent short-circuiting to be Gmax. An instance where the machining is normally performed is shown in FIG. 11. In FIG. 11, the relation among L, G and Gmax is represented in accordance with an expression that follows.
Gmax(2) less than L less than G(2)
where the number n enclosed by parentheses indicates the nth machining.
On the other hand, an instance where the discharge can not be effected owing to too large distance L between the surface of wire electrode and the workpiece before machining is shown in FIG. 12. In this case, the relation between L and G is represented by the following expression.
G(2) less than L
Also, an instance where the discharge is not effected due to too small distance L between the surface of wire electrode and the workpiece before machining to cause a short-circuit is shown in FIG. 13. In this case, the relation between L and Gmax is represented by the following expression.
L less than Gmax(2)
Herein, a method for calculating the wire electrode center path in the program analysis means 14 and displaying it on the display unit 17 before practical machining will be described below. FIG. 14 is a flow chart showing a drawing method of a program check provided inside the numerical control unit 13 of the conventional wire discharge machining apparatus, in which the program check comprises analysis means 21 for reading a command content from the content of a specified program, discrimination means 22 for discriminating whether or not the read command content is an end command, program analysis means 23 for calculating the machining position from the program content, and drawing means 24 for drawing the position analyzed by the program analysis means 23 on the display unit.
The operation will be described below. First, a command in the program specified is read by the analysis means 21 in FIG. 14. If it is discriminated by the discrimination means 22 that the read command is an end command, the program analysis means 23 calculates the machining position followed by the center of the wire electrode, and the drawing means 24 draws a locus with a constant thickness of line on the display unit.
An instance of drawing the locus with this method is shown in FIGS. 15 and 16. FIG. 15 shows a wire electrode center path when the machining is made once, and FIG. 16 shows the wire electrode center path when the machining is made three times.
The conventional wire discharge machining method and apparatus is configured in the above way. Since the drawing is only involved in the wire electrode center path, there was a problem that the finished surface could not be predicted. In the case where the machining is performed multiple times by varying the offset value in the same program, there was another problem that it was not possible to judge whether the sufficient discharge could be effected in each machining with the set correction amount.
This invention has been achieved to solve the above-mentioned problems, and it is a first object of the invention to provide a wire discharge machining method and apparatus which is enabled to discriminate whether or not the finish shape of machined workpiece is produced as specified visually every time of machining.
It is a second object of the invention to provide a wire discharge machining method and apparatus which is enabled to confirm visually the predicted discharge portion every time of machining and determine the correction amount effectively.
According to a first aspect of the invention, a wire discharge machining method includes adding a predicted discharge gap to the machining conditions and reading the amount of predicted discharge gap in doing a program check, and displaying the predicted discharge gap along with the wire electrode center path on a display unit.
According to a second aspect of the invention, a wire discharge machining apparatus comprises operation means for adding a predicted discharge gap to the machining conditions and reading the amount of predicted discharge gap in doing a program check, and drawing means for displaying the predicted discharge gap along with the wire electrode center path on a display unit.
According to a third aspect of the invention, the wire discharge machining apparatus according to the second aspect of the invention further comprises drawing means for displaying the predicted discharge gap along with the wire electrode center path on the display unit in a different color every time of machining.
According to a fourth aspect of the invention, a wire discharge machining method includes adding a predicted discharge gap to the machining conditions and reading the amount of predicted discharge gap in doing a program check, and displaying the wire electrode center path on a display unit as a thickness of the line drawing the (d+2xc3x97g)xc3x97drawing scale that is obtained from the predicated discharge gap g and the wire electrode diameter d.
According to a fifth aspect of the invention, a wire discharge machining apparatus comprises operation means for adding a predicted discharge gap to the machining conditions and reading the amount of predicted discharge gap in doing a program check, and drawing means for displaying the wire electrode center path on a display unit as a thickness of the line drawing the (d+2xc3x97g)xc3x97drawing scale that is obtained from the predicated discharge gap g and the wire electrode diameter d.
According to a sixth aspect of the invention, the wire discharge machining apparatus according to the fifth aspect of the invention further comprises drawing means for displaying the line indicating the wire electrode center path on the display unit in a different color every time of machining.
According to a seventh aspect of the invention, a wire discharge machining apparatus comprises drawing means for displaying a predicted discharge portion on a display unit.
According to an eighth aspect of the invention, the wire discharge machining apparatus according to the seventh aspect of the invention further comprises drawing means for displaying the line indicating the predicted discharge portion on the display unit in a different color every time of machining.
According to a ninth aspect of the invention, a wire discharge machining method includes adding a predicted discharge gap and a predicted minimum gap between the workpiece and a wire electrode to prevent short-circuiting to the machining conditions and reading the amounts of predicted discharge gap and predicted minimum gap in doing a program check, calculating a predicted allowance for machining in the nth machining from the predicted discharge gap, a correction amount of the wire electrode for the workpiece, and the wire electrode diameter, and displaying the predicted allowance for machining in the nth machining, and the predicted minimum gap for the nth machining between the workpiece and the wire electrode to prevent short-circuiting on a display unit.
According to a tenth aspect of the invention, a wire discharge machining apparatus comprises operation means for adding a predicted discharge gap and a predicted minimum gap between the workpiece and a wire electrode to prevent short-circuiting to the machining conditions and reading the amounts of predicted discharge gap and predicted minimum gap in doing a program check, operation means for calculating a predicted allowance for machining in the nth machining from the predicted discharge gap, a correction amount of the wire electrode for the workpiece, and the wire electrode diameter, and drawing means for displaying the predicted allowance for machining in the nth machining, and the predicted minimum gap for the nth machining between the work piece and the wire electrode to prevent short-circuiting on a display unit.
According to an eleventh aspect of the invention, the wire discharge machining apparatus according to the tenth aspect of the invention further comprises drawing means for displaying the line indicating the predicted allowance for machining on the display unit in a different color every time of machining.
According to a twelfth aspect of the invention, the wire discharge machining apparatus according to the eleventh aspect of the invention further comprises drawing means for displaying a portion where the predicted minimum gap for the nth machining between the workpiece and the wire electrode to prevent short-circuiting exceeds the predicted allowance for machining in the (nxe2x88x921) th machining on a display unit in a different color.